1. Field of the Invention
The present invention relates to a driving control circuit for an LED head in LED printers, particularly those for facsimile machines.
2. Description of the Prior Art
A conventional LED printer for printing a given character or figure on a recording paper using electrophotographic technology is equipped with an LED head comprising a plurality of LED elements arranged in a line, and each of the LED elements is energized corresponding to print data so as to emit light.
Dots each made by the light-emitting of each LED element form a print image.
The LED head comprises a plurality of register portions and a strobe generation circuit provided in the control portion of the printer supplies a strobe signal to each register portion to thereby restrain currents in each LED head.
Moreover, the LED printer comprises a smoothing circuit at the control portion thereof so as to form interpolation lines between original lines corresponding to the print data in order to enhance the resolution of print output.
That is, the smoothing circuit forms interpolation lines by interpolating black or white dots between original dots by matching an input data signal of M.times.N matrix with a previously set pattern.
For example, the smoothing circuit can perform A highly detailed printing, eliminating raggedness such as obliquely step-formed lines from a printed image by forming interpolation lines in the transferring direction of a recording paper so as to artificially supply print data of 200 dpi (dots per inch) to the LED head a pseudo print data of 400 dpi.
When printing is performed using the pseudo print data of 400 dpi formed by the smoothing circuit, the strobe generation circuit varies the strobe width for forming dots on interpolation lines from that for forming dots on original lines.
That is, the light-emitting of each LED element is reduced in intensity by shortening the strobe width for forming a dot on an interpolation line so as to form an electrostatic latent image corresponding to a small dot (i.e., a thin image).
Thus, it is possible to artificially improve resolution by interpolating input print data and making a printed image close to the original image the input data by forming the dots of original lines large and the dots of interpolation lines small.
However, when the smoothing circuit forms the interpolation line, white dots are liable to be formed in the interpolation line if black dots of the input data are not continuous to one another. As a result, when printing is performed after the interpolation lines are formed in the printed data, the printed image becomes thinner.
Whereas, when the black dots of the input print data are continuous to one another, black dots are liable to be formed in the interpolation line. As a result, when printing is performed after the interpolation lines are formed in the printed data, the printed image becomes darker.
Thus printer equipped with the smoothing circuit set forth above produces a thinner printed image from input data having a thin print image and a darker printed image from an input data having a dark print image so that the density of the printed image is varied from that of the original image.
When a printer used for a facsimile, a huge amount of print data has to be transferred in a short time so that the amount of each print data is reduced, resulting in the transference of print data of low resolution.
Such print data which vary in resolution causes different printed results and consequently the deteriorated quality of printed images.
Print data of low resolution can be interpolated by the smoothing means to be artificially improved in resolution. However, when print data of high resolution which has been received is interpolated similarly, the print data to be supplied to the LED head becomes too much and takes too much time in transference, so that the LED head cannot be driven in time.